Multiple Personality Disorder (MPD), now also known as Dissociative Iden- tity Disorder, raises many questions about the nature of persons, the goals of treatment, the suggestibility of patients, and the reliability of defendant reports of their own mental states. These issues become crucial when courts need to decide whether or not to punish a person with MPD who has committed a crime. This paper will explore that issue and propose a test of when people with MPD should be held criminally responsible.